In Lois Lowry's Gathering Blue, she used the word "tyke" instead of "boy" or "child". Do Americans use this word in a specific context? Her world in this novel is Darwinian, so I thought she might used some specific words to convey this Darwinian world.
To add to EJoshuaS's answer, "tyke" does have a colloquial or humorous connotation. I'm not familiar with this story, but if the word appears in dialogue then it's use is not important.
However, if it appears in the narrative, then Lowry may have intended for the word to have some importance: say, to reflect in some way the narrator's prejudices. Writers have been known to use language in that way to reveal things. But without specific examples, I can only speculate, & perhaps overthink an otherwise unimportant detail.